Stable loosely bounded asymmetric soliton molecules in fiber lasers

As an arising hotspot in nonlinear science, soliton molecules are found to have intriguing internal dynamics originating from the nonlinear interactions between closely spaced pulses. In dissipative systems with saturable gain and loss, the soliton molecule composed of unequal pulses is inferred to be unstable due to the soliton-energy-quantization effect. We experimentally demonstrated the stable soliton molecule in the form of two long-range unequal solitons trapped by the dispersive waves, i.e., the loosely bounded asymmetric soliton molecules, and numerically explored its intracavity evolution dynamics and stability mechanism. Under the nonlinear attraction of guiding-center-soliton, both solitons have average parameters satisfying the fundamental soliton, facilitating the stable evolution of asymmetric soliton molecules. Our work sheds light on the symmetry-broken of the localized structures in nonlinear-dissipative systems, which has the potential to enhance the data-carrying capacity of optical communications.